The present invention relates to a speaker diaphragm. More specifically, the present invention relates to a speaker diaphragm that has excellent acoustic characteristics and is produced with high production efficiency.
Conventionally, speaker diaphragms are known that can be obtained by impregnating a substrate with a thermosetting resin and subjecting the resultant substrate to molding and curing. Known substrates include a plain-woven fabric made of rigid reinforced fibers such as carbon fibers (CF) and glass fibers (GF), and a nonwoven fabric obtained by coating chopped pieces of fibers, such as CF and GF, with a resin and bonding the fibers randomly. As the impregnant thermosetting resin (matrix resin), an epoxy resin is known.
CF and GF used for the substrate have a large modulus of elasticity but are rigid and have extremely small internal loss. The epoxy resin as the matrix resin has little toughness and internal loss. Therefore, the conventional speaker diaphragm obtained by this combination of the substrate and the matrix resin generates large and sharp resonance. This type of speaker diaphragm is therefore insufficient for use for a full-range speaker. If a woven fabric is used as the substrate, there arise the problems that the physical properties of the diaphragm are likely to change depending on the directionality of the weaving of the woven fabric (anisotropy in the longitudinal and lateral directions) and that a texture of the fabric may be non-uniformly deformed during molding, resulting in non-uniform acoustic characteristics.
Another speaker diaphragm that has been proposed is formed by fusing thermoplastic resin fibers by heat pressing. However, this proposal has the problems that since a thermoplastic resin has a low modulus of elasticity, it is difficult to obtain a diaphragm with good properties (for example, a high Young""s modulus), and that the heat resistance is insufficient.
In order to solve the above problems, a diaphragm has recently been developed, that is produced by binding a nonwoven fabric made of organic fibers having a high modulus of elasticity with a matrix resin or a binder. In this way, attempts to improve the characteristics (for example, the internal loss) of the diaphragm have been increasingly actively made.
However, the diaphragm obtained from a nonwoven fabric made of organic fibers having a high modulus of elasticity has the problems that, because the strength of the nonwoven fabric is low, its handling is not easy and the acoustic characteristics fail to be uniform.
Known methods for forming a nonwoven fabric from the organic fibers having a high modulus of elasticity, include the chemical bonding method and the needle punching method. The chemical bonding method tends to generate wrinkles and cracks, causing the problem of insufficient acoustic characteristics. The needle punching method possesses the problem that the physical properties of the resultant diaphragm may depend on the direction of webs constituting the nonwoven fabric. A filler may be added to the matrix resin or the binder as required. However, the conventional combination of the matrix resin and the filler fails to provide a sufficient internal loss and increases the density of the diaphragm. Moreover, as is well known, the workability of the matrix resin used for the diaphragm is poor.
As described above, conventional speaker diaphragms have problems yet to be solved with regard to acoustic characteristics such as the modulus of elasticity and the internal loss, as well as with regard to production efficiency.
The present invention has been made to solve the above conventional problems. An object of the invention is to provide a speaker diaphragm that has excellent acoustic characteristics and is produced with high production efficiency.
The speaker diaphragm of the present invention has one or two or more layers of nonwoven fabric, the nonwoven fabric layer being impregnated with a thermosetting resin composition, molded, and cured, wherein at least one of the nonwoven fabric layers is formed of nonwoven fabric made of a fiber material containing protein fibers, and the thermosetting resin composition contains an unsaturated polyester resin as a main component.
In a preferred embodiment, the protein fibers are silk fibers made of a natural silk, in which sericin has been substantially removed from the outer surface.
In a preferred embodiment, the content of the sericin in the silk fibers is 1% by weight or less.
In a preferred embodiment, the fineness of the silk fibers is 0.8 to 1.2 denier.
In a preferred embodiment, the speaker diaphragm has a plurality of nonwoven layers and the plurality of nonwoven fabric layers include a nonwoven fabric layer formed of the silk fibers and a nonwoven fabric layer formed of organic fibers having a high modulus of elasticity.
In a preferred embodiment, the organic fibers having a high modulus of elasticity are meta-aramid fibers.
In a preferred embodiment, in the speaker diaphragm of the present invention, the nonwoven fabric layer formed of the silk fibers and the nonwoven fabric layer formed of the organic fibers having a high modulus of elasticity are layered alternately.
In a preferred embodiment, the nonwoven fabric is meshed.
In a preferred embodiment, the thermosetting resin composition contains a scaly mineral.
In a preferred embodiment, the scaly mineral is graphite.
In a preferred embodiment, the graphite has a mean grain diameter in a range of 4 to 10 xcexcm.
In a preferred embodiment, the scaly mineral is contained in a range of 20 to 50 parts by weight for 100 parts by weight of the unsaturated polyester resin.
In a preferred embodiment, the thermosetting resin composition further contains microbaloons.
In a preferred embodiment, the microbaloons are selected from organic microbaloons containing a vinylidene chloride-acrylonitrile copolymer as a main component and inorganic microbaloons containing borosilicate glass as a main component.
In a preferred embodiment, the microbaloons are contained in a range of 5 to 20 parts by weight for 100 parts by weight of the unsaturated polyester resin.